The erosion behavior of a nanocomposite W-Cu material under arc breakdown was investigated. The arc erosion rates of the material were determined, and the eroded surfaces and arc erosion mechanisms were studied by scanning electron microscopy. It is concluded that the nanocomposite W-Cu electrical contact material shows a characteristic of spreading arcs. The arc breakdown of a commercially used W-Cu alloy was limited in a few areas, and its average arc erosion rate is twice as large as that of the former. Furthermore, it is also proved that the arc extinction ability and arc stability of the nanocomposite W-Cu material are excellent, and melting is the major failure modality in the make-and-break operation of arcs.